1. Field of the Invention
The invention relates to a method of manufacturing a non-aqueous electrolyte secondary battery. More specifically, the invention relates to a manufacturing method that is designed for a non-aqueous electrolyte secondary battery equipped with a wound electrode body and includes an aging treatment. Also, the invention relates to a non-aqueous electrolyte secondary battery.
2. Description of Related Art
Chargeable/dischargeable non-aqueous electrolyte secondary batteries such as nickel hydride batteries, lithium secondary batteries and the like have been increasing in importance as in-vehicle power supplies, power supplies of personal computers and mobile terminals, and the like. In particular, lithium secondary batteries that are light and make it possible to obtain high energy density have been preferably used as in-vehicle high-output power supplies.
As one form of such batteries, a tightly closed battery in which an electrode body that is obtained by laminating a positive electrode and a negative electrode on each other via a separator is accommodated in a battery case together with an electrolyte can be mentioned. Typically, after a wound electrode body that is obtained by winding a sheet-like electrode body is accommodated in the battery case, the battery case is fitted with a lid body to be sealed, whereby this tightly closed battery is structured. Then, the structured battery is subjected to a charge/discharge treatment (a conditioning treatment) on a predetermined condition in order to make an adjustment such that the structured battery can be actually employed. Besides, after the aforementioned conditioning treatment is performed, an aging treatment in which the battery is retained under a predetermined condition is performed for the purpose of obtaining various effects such as infiltrating a non-aqueous electrolytic solution into the wound electrode body, selecting a battery in which the drop in initial battery capacity that can be equivalent to a self-discharge amount (the initial deterioration) is large, and also stabilizing the battery performance, etc. This aging treatment depends on its purpose, but can be performed in a temperature range higher than a room temperature range (e.g., 30° C. to 60° C.), whereby the aforementioned retention time until a predetermined effect is obtained can be ended as a short time.
In the aging treatment at a relatively high temperature as in this case, it is known that problems can occur in that the internal resistance of the battery rises as an inhibitory substance is produced as a result of a charge/discharge reaction of the battery, or as an electrode active material swells etc., that the internal pressure of the battery is enhanced due to gas generated during aging so that the battery case is deformed, and the like. On the other hand, it is disclosed in, for example, Japanese Patent Application Publication No. 2010-153337 (JP-2010-153337 A) that the internal resistance of the battery and the internal pressure of the battery are restrained from rising by adjusting the concentration of oxygen gas in the battery during aging to 10 vol % to 20 vol %.
By the way, the aging treatment in manufacturing the secondary battery can also be performed for the purpose of dissolving/precipitating metal foreign matters that can be mixed into the battery in a manufacturing process. In the aging treatment that is performed for this purpose, it has been conventional to adjust the battery to a high state of charge (SOC) after the conditioning treatment, and hold the battery at a high temperature for a long time (e.g., for about 24 hours or more). In this aging treatment, the dissolution of metal foreign matters can further be promoted, the holding time until the achievement of a predetermined effect can further be reduced, and a reduction in the costs of manufacturing can be expected by holding the temperature at which the battery is held at a higher temperature, for example, within a temperature range equal to or higher than 60° C.